Background: Recent studies of neuroendocrine tumor cell lines suggest that ras/raf-1 activation could be detrimental to tumorigenesis. The mechanism by which it alters neuroendocrine tumor cells is unclear. We hypothesize that activation of the ras/raf signal transduction pathway may alter gastrointestinal carcinoid cells by inducing morphologic transdifferentiation.
Methods: Pancreatic carcinoid (BON) cells were transduced in a stable manner with an estrogen inducible raf-1 fusion protein (creating "BON-raf cells"). BON and BON-raf cells were then treated with either control or 1 micromol/L estradiol (E2). Western blots were used to confirm the phosphorylation of extracellular signal-regulated kinase 1/2. Morphologic changes were evaluated using light and electron microscopy.
Results: Western blots using antibodies against phosphorylated and unphosphorylated extracellular signal-regulated kinase 1/2. confirmed that phosphorylation was only present in the BON-raf E2 cells. BON cells treated with control and E2 and BON-raf cells treated with control all looked identical in culture. After treatment with E2 to induce raf-1, the BON-raf cells underwent dramatic morphologic changes. Under light and electron microscopy the cells became flatter and developed much sharper cellular borders mimicking cellular differentiation.
Conclusions: Activation of the ras/raf-1 signal transduction pathway leads to prominent phenotypic changes that resemble differentiation of gastrointestinal carcinoid cells in vitro.